diff --git a/src/lib/actions/inference-set-degraded-state.test.ts b/src/lib/actions/inference-set-degraded-state.test.ts
index d2528c03677..552279ee35f 100644
--- a/src/lib/actions/inference-set-degraded-state.test.ts
+++ b/src/lib/actions/inference-set-degraded-state.test.ts
@@ -2,35 +2,50 @@
 // SPDX-License-Identifier: Apache-2.0
 
 import { describe, expect, it } from "vitest";
+import { SandboxConfigError } from "../sandbox/config";
 import type { ConfigObject } from "../security/credential-filter";
-import { runInferenceSet } from "./inference-set";
+import { InferenceSetError, runInferenceSet } from "./inference-set";
 import { baseSession, createDeps } from "./inference-set.test-support";
 
 describe("runInferenceSet degraded state handling", () => {
-  it("keeps gateway and registry consistent when the sandbox config read fails", async () => {
+  it("aborts before mutating any layer when the sandbox config read fails (#6997)", async () => {
     const deps = createDeps({ config: {}, session: baseSession() });
+    // A stopped sandbox surfaces SandboxConfigError from the in-sandbox read —
+    // the exact path from the issue.
     deps.calls.readSandboxConfig.mockImplementation(() => {
-      throw new Error("sandbox config unreadable");
+      throw new SandboxConfigError([
+        "  Cannot read openclaw config (/sandbox/.openclaw/openclaw.json).",
+        "  Is the sandbox running?",
+      ]);
     });
 
-    await expect(
-      runInferenceSet(
-        { provider: "nvidia-prod", model: "nvidia/nemotron-3-super-120b-a12b", noVerify: true },
-        deps,
-      ),
-    ).rejects.toThrow("sandbox config unreadable");
+    const error = await runInferenceSet(
+      { provider: "nvidia-prod", model: "nvidia/nemotron-3-super-120b-a12b", noVerify: true },
+      deps,
+    ).then(
+      () => {
+        throw new Error("expected runInferenceSet to reject");
+      },
+      (rejection: unknown) => rejection,
+    );
 
-    expect(deps.calls.updateSandbox).toHaveBeenCalledWith(
-      "alpha",
-      expect.objectContaining({
-        provider: "nvidia-prod",
-        model: "nvidia/nemotron-3-super-120b-a12b",
-        endpointUrl: null,
-        credentialEnv: null,
-        preferredInferenceApi: null,
-        nimContainer: null,
-      }),
+    // Converted to the command-layer error type with an actionable message, so
+    // the CLI reports cleanly instead of dumping a raw SandboxConfigError stack.
+    expect(error).toBeInstanceOf(InferenceSetError);
+    expect((error as Error).message).toMatch(/Is the sandbox running/);
+    expect((error as Error).message).toMatch(/Start the sandbox and retry/);
+
+    // #6997 core guarantee: the read is a pre-flight gate, so a stopped sandbox
+    // leaves EVERY mutable layer untouched. Previously the read ran after the
+    // gateway route and registry were committed, leaving a half-applied switch.
+    // Assert zero mutation so re-ordering the read back after the mutations
+    // regresses this test. (The read-only `openshell provider get` probe that
+    // runs earlier is not a mutation, so filter to the route-SET call.)
+    const routeSetCalls = deps.calls.captureOpenshell.mock.calls.filter(
+      (args) => Array.isArray(args[0]) && args[0][0] === "inference" && args[0][1] === "set",
     );
+    expect(routeSetCalls).toHaveLength(0);
+    expect(deps.calls.updateSandbox).not.toHaveBeenCalled();
     expect(deps.calls.writeSandboxConfig).not.toHaveBeenCalled();
     expect(deps.calls.restartSandboxGateway).not.toHaveBeenCalled();
   });
diff --git a/src/lib/actions/inference-set.ts b/src/lib/actions/inference-set.ts
index b6c5dccf259..9b1275cda94 100644
--- a/src/lib/actions/inference-set.ts
+++ b/src/lib/actions/inference-set.ts
@@ -34,6 +34,7 @@ import {
   recomputeSandboxConfigHash,
   resolveAgentConfig,
   rewriteConfigUrlsWithDnsPinning,
+  SandboxConfigError,
   seedHermesDashboardConfig,
   writeSandboxConfig,
 } from "../sandbox/config";
@@ -573,6 +574,36 @@ function assertHermesCompatibleAnthropicOpenAiProvider(
   );
 }
 
+/**
+ * Read the in-sandbox agent config, converting a `SandboxConfigError` (the
+ * in-sandbox config could not be read or parsed — most commonly because the
+ * sandbox container is stopped) into a clean `InferenceSetError`. Callers use
+ * this as a pre-flight gate before the gateway route and registry are mutated,
+ * so an unreadable config aborts the command cleanly instead of crashing with a
+ * raw stack after a half-applied switch (#6997).
+ */
+export function readInSandboxConfigOrFail(
+  deps: Pick<InferenceSetDeps, "readSandboxConfig">,
+  sandboxName: string,
+  target: AgentConfigTarget,
+): ConfigObject {
+  try {
+    return deps.readSandboxConfig(sandboxName, target);
+  } catch (error) {
+    if (error instanceof SandboxConfigError) {
+      const lines = [...error.lines];
+      // `readSandboxConfig` also raises this for a corrupt/unparseable config,
+      // which starting the sandbox would NOT fix — only add the start hint for
+      // the stopped-sandbox case (the one that asks "Is the sandbox running?").
+      if (lines.some((line) => /is the sandbox running/i.test(line))) {
+        lines.push("  Start the sandbox and retry.");
+      }
+      throw new InferenceSetError(lines.join("\n"), error.exitCode);
+    }
+    throw error;
+  }
+}
+
 async function runInferenceSetWithoutHostLock(
   options: InferenceSetOptions,
   deps: InferenceSetDeps,
@@ -750,6 +781,13 @@ async function runInferenceSetWithoutHostLock(
     deps,
   );
 
+  // Read the in-sandbox config *before* mutating the gateway route or registry.
+  // If it is unreadable (e.g. a stopped sandbox), the mutations below would have
+  // committed the gateway route and registry first (only the in-sandbox layer is
+  // `rebuild`-recoverable), so gate on the read here to abort cleanly instead of
+  // leaving a half-applied switch across the three config layers (#6997).
+  const config = readInSandboxConfigOrFail(deps, sandboxName, target);
+
   deps.log(`  Setting OpenShell inference route: ${provider} / ${model}`);
   const setResult = deps.captureOpenshell(
     openshellInferenceSetArgs({
@@ -795,7 +833,6 @@ async function runInferenceSetWithoutHostLock(
     throw new InferenceSetError(`Failed to update NemoClaw registry for sandbox '${sandboxName}'.`);
   }
 
-  const config = deps.readSandboxConfig(sandboxName, target);
   const previousOpenClawInferenceApi = readPreviousOpenClawInferenceApi(agentName, config);
   const preferredInferenceApi =
     explicitPreferredInferenceApi ??
diff --git a/test/inference-set-preflight.test.ts b/test/inference-set-preflight.test.ts
new file mode 100644
index 00000000000..f616e3d86f6
--- /dev/null
+++ b/test/inference-set-preflight.test.ts
@@ -0,0 +1,83 @@
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+import { describe, expect, it, vi } from "vitest";
+
+import { InferenceSetError, readInSandboxConfigOrFail } from "../src/lib/actions/inference-set";
+import type { AgentConfigTarget } from "../src/lib/sandbox/config";
+import { SandboxConfigError } from "../src/lib/sandbox/config";
+import type { ConfigObject } from "../src/lib/security/credential-filter";
+
+const TARGET = {
+  agentName: "openclaw",
+  configPath: "/sandbox/.openclaw/openclaw.json",
+} as unknown as AgentConfigTarget;
+
+describe("readInSandboxConfigOrFail pre-flight gate (#6997)", () => {
+  it("returns the config when the sandbox is readable", () => {
+    const config = { model: "old" } as unknown as ConfigObject;
+    const readSandboxConfig = vi.fn(() => config);
+
+    const result = readInSandboxConfigOrFail({ readSandboxConfig }, "box", TARGET);
+
+    expect(result).toBe(config);
+    expect(readSandboxConfig).toHaveBeenCalledWith("box", TARGET);
+  });
+
+  it("converts a stopped-sandbox SandboxConfigError into an actionable InferenceSetError", () => {
+    const readSandboxConfig = vi.fn(() => {
+      throw new SandboxConfigError(
+        [
+          "  Cannot read openclaw config (/sandbox/.openclaw/openclaw.json).",
+          "  Is the sandbox running?",
+        ],
+        3,
+      );
+    });
+
+    let thrown: unknown;
+    try {
+      readInSandboxConfigOrFail({ readSandboxConfig }, "box", TARGET);
+    } catch (error) {
+      thrown = error;
+    }
+
+    // Must be the command-layer error type so it is handled cleanly (no raw stack).
+    expect(thrown).toBeInstanceOf(InferenceSetError);
+    const err = thrown as InferenceSetError;
+    // Preserves the original diagnostic lines and the recorded exit code...
+    expect(err.message).toContain("Is the sandbox running?");
+    expect(err.exitCode).toBe(3);
+    // ...and adds the actionable next step.
+    expect(err.message).toContain("Start the sandbox and retry");
+  });
+
+  it("omits the start-sandbox hint for a non-stopped config error (e.g. parse failure)", () => {
+    // A corrupt/unparseable config raises SandboxConfigError too, but starting
+    // the sandbox would not fix it — the start hint must not be appended.
+    const readSandboxConfig = vi.fn(() => {
+      throw new SandboxConfigError(["  Failed to parse openclaw config: unexpected token."], 1);
+    });
+
+    let thrown: unknown;
+    try {
+      readInSandboxConfigOrFail({ readSandboxConfig }, "box", TARGET);
+    } catch (error) {
+      thrown = error;
+    }
+
+    expect(thrown).toBeInstanceOf(InferenceSetError);
+    const err = thrown as InferenceSetError;
+    expect(err.message).toContain("Failed to parse");
+    expect(err.message).not.toContain("Start the sandbox and retry");
+  });
+
+  it("does not swallow unrelated errors", () => {
+    const boom = new TypeError("unexpected");
+    const readSandboxConfig = vi.fn(() => {
+      throw boom;
+    });
+
+    expect(() => readInSandboxConfigOrFail({ readSandboxConfig }, "box", TARGET)).toThrow(boom);
+  });
+});